Silicon carbide (SiC) is considered to be capable of achieving high-temperature resistance, high voltage resistance, high-frequency resistance, and high environment resistance each of which could not be achieved by conventional semiconductor materials, such as silicon (Si) and gallium arsenide (GaAs). Therefore, silicon carbide is expected as a semiconductor material for next-generation power devices and a semiconductor material for high-frequency devices.
The seeded sublimation growth method (modified Lely method) is conventionally proposed as a method for growing a monocrystalline silicon carbide, such as for example in Patent Literature 1 below. In this modified Lely method, a seed material made of a monocrystalline silicon carbide is placed in a low-temperature zone of a crucible and a powder of source material containing Si as a source material is placed in a high-temperature zone thereof. Then, the interior of the crucible is brought into an inert atmosphere and heated to a high temperature of 1450° C. to 2400° C. to sublimate the powder of source material placed in the high-temperature zone. As a result, silicon carbide can be epitaxially grown on the surface of the seed material placed in the low-temperature zone.
Nevertheless, the modified Lely method is a method of growing silicon carbide crystals by providing a temperature gradient in the gas phase. Therefore, in the case of using the modified Lely method, a large apparatus is required for epitaxial growth of silicon carbide and the process for epitaxial growth of silicon carbide is difficult to control. This presents a problem of rise in cost of producing a silicon carbide epitaxial growth film. In addition, epitaxial growth of silicon carbide in the gas phase is nonequilibrium. Therefore, crystal defects are likely to occur in the silicon carbide epitaxial growth film being formed and there also arises a problem of ease of roughening of the crystal structure.
An example of a method for epitaxial growth of silicon carbide other than the modified Lely method is metastable solvent epitaxy (MSE) which is a method of epitaxially growing silicon carbide in the liquid phase, as proposed for example in Patent Literature 2.
In MSE, a seed material made of a crystalline silicon carbide, such as a monocrystalline silicon carbide or a polycrystalline silicon carbide, and a feed material made of silicon carbide are faced each other at a distance as small as, for example, 100 μm or less and a Si melt layer is interposed between them. Then, these materials are subjected to heating treatment in a vacuum, high-temperature environment to epitaxially grow silicon carbide on the surface of the seed material.
It is considered that in MSE a difference in chemical potential between the seed material and the feed material causes a concentration gradient of carbon dissolved in the Si melt layer and thus a silicon carbide epitaxial growth film is formed. Therefore, unlike the case of using the modified Lely method, there is not necessarily a need to provide a temperature difference between the seed material and the feed material. Hence, with the use of MSE, not only the process for epitaxial growth of silicon carbide can be easily controlled with a simple apparatus but also a high-quality silicon carbide epitaxial growth film can be stably formed.
In addition, MSE also has the advantage of being capable of forming a silicon carbide epitaxial growth film even on a large-area seed substrate and the advantage of lowering the temperature for the process of epitaxially growing silicon carbide because the extremely small thickness of the Si melt layer facilitates the diffusion of carbon from the feed material.
Accordingly, MSE is considered to be an extremely useful method as the method for epitaxial growth of a monocrystalline silicon carbide and active research on MSE has been carried out.